Bools and explicitness [was Re: PyWart: The problem with "print"]

[Chris Angelico]

On Fri, Jun 7, 2013 at 1:35 AM, Robert Kern <robert.kern at gmail.com> wrote:
> On 2013-06-06 10:45, Chris Angelico wrote:
>
>> For the "accept any object that has a next() method" sorts of rules, I
>> don't know of any really viable system that does that usefully. The
>> concept of implementing interfaces in Java comes close, but the class
>> author has to declare that it's implementing some named interface. In
>> theory there could be something that deduces the validity from the
>> given structure, but I'm not aware of any language that does this. But
>> it would let you do stuff like this (prototyped in Python):
>
>
> As Serhiy notes, Go does this, almost exactly as you wrote it (modulo
> syntax).
>
> http://golang.org/doc/effective_go.html#interfaces_and_types

Thanks (and thanks for actually providing a link). Many years ago I
came to the conclusion that anything I could conceive in language
design has already been done somewhere :)

Anyway, regardless of your language, there's always some criteria that
can't be coded. Suppose the valid input for a function were "integers
whose square roots are integers but whose cube roots are not". You
won't easily get compile-time checking of that.

ChrisA